PROJECT SUMMARY DNA methylation is a key epigenetic regulator of gene expression and is essential for embryonic development and cell differentiation. Aberrant DNA methylation patterning, a hallmark of nearly all human cancers, is a major contributor to tumor suppressor gene silencing and genomic instability that promotes cancer development and progression. The epigenetic oncoprotein UHRF1 is intimately linked to the control of DNA methylation through recruitment of the maintenance DNA methyltransferase DNMT1 to replicating chromatin. UHRF1 is frequently upregulated in human cancers and its depletion in model systems has demonstrated tumor suppressive effects. These studies have motivated intense recent analysis of UHRF1 biological/pathological function and have sparked clinical interest in the development of UHRF1 inhibitors for cancer therapy. A recently described interaction between UHRF1 and DNA ligase 1 (LIG1) established LIG1 as a novel regulator of DNA methylation and presents a potentially exploitable chromatin-targeting mechanism for UHRF1. The overall goal of the F99 phase of this fellowship is to determine the role of LIG1 in UHRF1 molecular and oncogenic functions. Specifically, the Aims are 1a) to determine the role of LIG1 in DNA methylation maintenance and 1b) evaluate the therapeutic potential of disrupting the UHRF1-LIG1 interaction. The training objectives of the F99 phase include building expertise in technologies of CRISPR/Cas9 genome editing, genomic and epigenomic data analysis, and cancer cell biology. The K00 phase of this fellowship (Aim 2), will define the impact of microorganisms and their metabolites on epigenetic signaling in colorectal cancer. Intestinal organoids and mouse models of intestinal cancer will be used to determine if the gut microfloral metabolism elicits transcriptional responses in host cancer cells. Data and training acquired in this phase will focus my trajectory toward leading an interdisciplinary cancer research lab studying the symbiotic and pathogenic relationship between the microbiome and host epigenome in human health and cancer.